stage is making headlines tonight. We saw her testify before congress, wearing the glasses she's been wearing. They turn out to be another consequences of that serious concussion and blood clot. Jonathan karl tells us what the administration confirmed today. Reporter: We learned something new today about what hillary clinton was going through when she gave that tough testimony on capitol hill this week. What difference, at this point, does it make! Those glasses she was wearing were though fashion statement. If you look closer in the left lens notice those vertical lines. Those lines are an indication she's still dealing with side effects from the concussion she's suffered six weeks ago. When you're used to having single vision all of your life and all of a sudden the muscles aren't in balance and the double vision is extremely noticeable and bothersome. Reporter: Her glasses have a fresnel prism lens. Used to assist people having double vision. Earlier this week the state department deflected questions about the glasses. Pointing reporters to this interview from last summer, suggesting they were a fashion choice. I feel so relieved to be at the stage I'm at in my life right now. If I to want wear my glasses, I'm wearing my glasses. Reporter: She's been wearing them since last month after doctors discovered a blot clot close to her brain. Today the state department confirmed there are lingering issues from her concussion, however the secretary seems to be taking it all in stride. She also enjoys some of the comments she saw in the press about the extra diplomatic lift she gets from gesturing with them. Doctors tells us double vision is common after a concussion, but it's usually temporary and clears up after a few weeks or a month. Concussion or not, secretary clinton seemed at top of her game. In five hours of tough grueling testimony on wednesday, she was as forceful and in charge as we have ever seen her. All right, johnathan carl, reporting from washington. Thanks. This just in, a big move

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